The power amplification of electrical signals is an often necessary task, especially if signals are transmitted over long distances (e.g. wireless). For example, the power amplifier (PA) in a mobile terminal has to cope with a wide range of load impedances, since the antenna impedance is heavily affected by instantaneous environmental conditions (e.g. free space, antenna covered by hand). Many power amplifiers are optimized for 50Ω conditions and also power amplifier specification may not care about mismatch (e.g. despite requirements for ruggedness and stability). For instance, the power variation into a non-50Ω antenna load may be neglected, which increases the effort for antenna and radio frequency (RF) engine design (e.g. to optimize post power amplifier matching and antenna matching).
Since the radiated power is often not satisfying, the network operators started to define specific requirements (so-called total radiated power requirements, TRP), especially in area where the coverage is minimal. One related requirement may be the power variation into voltage standing wave ratio (VSWR, output power ripple caused by non-50Ω antenna impedance). It is desired to minimize the power variation into mismatch.